In recent years, high image quality of electrophotographic image forming apparatuses has increasingly been demanded.
As to an apparatus for image formation, a method by which a digital method is employed, writing in the digital method is conducted by using a light source typified by semiconductor laser, and an image is obtained via reverse development becomes mainstream.
Since a semiconductor laser source exhibits coherency, reflected light from the layer interface of a photoreceptor and from a substrate causes complicated interference, whereby there appears a problem such that image defects referred to as so-called moire are generated.
Correspondingly, various techniques to improve the photoreceptor have been investigated so far.
For example, there are a method of cutting the surface of a conductive substrate with a bite, and a method of conducting a blast treatment for roughening the surface to appropriately scatter light, but there appears problems such that in the former case, burr is produced during a cutting work, resulting in generation of image defects, and in the latter case, impurities are penetrated into the substrate via the blast treatment, resulting in generation of image defects.
In this case, a technique by which metal oxide particles typified by titanium dioxide particles are dispersed and contained in an intermediate layer of the photoreceptor to scatter light appropriately in a subbing layer has been actively studied (refer to Patent Documents 1 and 2). However, when the titanium dioxide content is increased in order to improve moire resistance, produced is a problem such that titanium dioxide particles are partially coagulated in the intermediate layer, and a bridging structure is formed in the layer, whereby leakage of charge through the above-described portion is generated in the case of application to the photoreceptor. In order to solve this problem, the surface of titanium dioxide is subjected to an organic or inorganic treatment to increase electrical resistance, and a binder resin in the intermediate layer is designed to be set to high resistance, but results obtained via these trials are still insufficient. Accordingly, reduction of moire resistance and black spot defects has not still been satisfied at the same time in the case of an electrophotographic photoreceptor used in an image forming apparatus fitted with an inherent light source, resulting in a big problem to be solved.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 4-303846
(Patent Document 2) Japanese Patent O.P.I. Publication No. 8-328283